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Why our Solar System May be Unique in the Milky Way

We're not alone in the universe but we may be lonelier than we thought.

On
the surface, our solar system appears to be fairly typical. While we continue to learn surprising new
things about the family of planets and moons who share our sun, we've always
been relatively confident that our solar system was no different than any other
solar system we could imagine. This was
largely due to a Copernican Principle that held that celestial bodies shared
certain behaviours and dynamics.

However,
some new evidence related to the discovery of exoplanets orbiting distant
stars is beginning to challenge that Copernican view. The primary motivation for the search for
exoplanets is to assess the potential for other life or intelligent life in the Milky Way
Galaxy.

To
date, 1,713 exoplanets around 1,042 Starshave
been potentially discovered orbiting various stars at various distances from
their suns. These observations have been
made by both land-based telescopes and satellites such as the Kepler Spacecraft. They detect exoplanets by noting the wobble of a star
as the orbiting planet or planets affect its motion, the bending or shifting of
light from the star as a result of the planets gravity, and the relative
brightness of the star as planets pass in front of it and reduce its luminosity.

Directly imaged planet by ESO/A.-M. Lagrange

Past Assumptions are
Wrong

Some
surprises have emerged that have led us to conclude that our solar system's
design and dynamics may not be so common after all. For one, we have always assumed that a solar
system would have smaller, rocky planets orbiting closer to a star, and larger
gas giants would occupy the outer rings of orbit further away from the star.

We
also assumed that most solar systems would have the clean, circular orbits that
our solar system possesses, and that the planets would be nicely spaced at a
comfortable distance from each other, and to some degree from the sun or star.

Widely varying orbits discovered by Kepler. Image credit: NASA

In
addition, we seem to assume that only one star stands at the center of a solar
system when in fact 85% of the stars in our galaxy are binary-stars with one star
orbiting the other in very close proximity.

What
is becoming apparent is that none of those assumptions are apparent in the
empirical evidence coming from distant exoplanet observations. In fact, it's beginning to appear that our
solar system is distinctly unique from many of the patterns emerging from other
systems and the exoplanets that define them.
For the record, most of the exoplanet systems studied have been around
solitary-stars rather than binary-stars.

The New and Emerging
Patterns

One
of the patterns that has begun to emerge is the preponderance of gas-giants exceeding the
numbers we had originally assumed. Some
of these gas giants are significantly larger than Jupiter, some are in
surprisingly close orbits to the their stars and are referred to as
"Hot-Jupiters," and many are smaller, gaseous planets called
"Mini-Neptunes."

A Year in a Day?

But
it's not just the size and number that was surprising but the very close orbits
of these gas-giants to their stars. For
instance, five enormous gas-giants orbit
a star within one-twelfth the size of the orbit of Earth to our sun, and
complete their orbits in a matter of days and weeks as opposed to months or
years. That doesn't sound anywhere
close to the dynamics or our solar system.

Rare Earths

Another
factor is that the occurrence of rocky or "Earth-like" planets are
not as prevalent as presumed, and many are significantly larger than Earth and
are definitely not Earth-like. This
particular "Super-Earth" exoplanet is five times the size of earth,
and orbits so close to it's star that the temperature on the surface is 1,200°
C or 2,200°F. That's hot enough to melt
gold.

To
date, only one truly Earth-like planet in the habitable or
"Goldilocks Zone" of orbit has been found. It's believed it could possess liquid water
given its position in a habitable zone but the technology does not yet exist to
verify this with certainty.

Kepler 186-f, the most Earth like planet. An artist’s impression by NASA Ames/SETI Institute/JPL-Caltech

Wild Orbits

Another
factor contradicts the well-spaced dispersal and relatively uniform circular
orbits of the 8 primary planets across a parallel plain in our solar
system. Other solar systems demonstrate
elongated, elliptical orbits that follow unique plains of orbit around their
star. Wild
orbits
that often follow paths opposite to each other.
This would create a chaotic environment resulting in heavy bombardment
of meteors, asteroids and comets on the exoplanets on a regular basis. It also raises the on-going potential for
planetary collisions. Collisions with
celestial objects such as asteroids and comets is a fear we all share, but
usually separated by millions of years rather than a constant event.

Of
course our view of other solar systems may change as we get better at
discovering exoplanets. It is much easier to discover a large planet than a
small planet and the nearer the planet is to its star the more often it will
pass in front of the star making it easier to detect also. Time will tell us
more.

Is Anybody Out There?

In
the meantime, the search continues. It's
hard to know if or when we'll ever be able to travel to the elusive Earth-like
planets we're searching for, but it's fascinating to wonder what's out there.

The
implications affect many of our ideas about how prevalent intelligent life, let
alone any life may be in the universe.
It's preposterous to assume that we are totally alone in the universe,
but we may be lonelier than we thought.